Optically Transparent Superhydrophobic Thin Film

ABSTRACT

A composition that is easily applied, clear, well-bonded, and superhydrophobic is disclosed. In one aspect, the composition includes a hydrophobic fluorinated solvent, a binder comprising a hydrophobic fluorinated polymer, and hydrophobic fumed silica nanoparticles. Also disclosed is a structure including a substrate coated with the composition, as well as a method for making the composition and a method of coating a substrate with the composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/991,873, filed May 29, 2018, which claims priority to U.S.Provisional Application No. 62/635,993 filed on Feb. 27, 2018. Theforegoing applications are incorporated herein by reference.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Superhydrophobic surfaces and coatings having exceptional waterrepellency properties have potential application in numerous fields ofendeavor. Well-bonded, optically clear coatings have been achieved, ashave optically clear, superhydrophobic coatings. But there remains aneed for an easily applied, optically clear, well-bonded,superhydrophobic coating or thin film. This is because the physicalproperties that can achieve these three characteristics tend to bemutually exclusive when using conventional thin film materials andmethods. For example, a superhydrophobic material typically has a micro-to nanometer surface roughness, which tends to scatter light and makesoptical clarity difficult to achieve. Likewise, materials with highoptical clarity tend to have low surface roughness (i.e., a very smoothsurface) and do not usually allow good bonding to low surface energyhydrophobic materials.

SUMMARY

In one aspect, the present disclosure provides a composition including ahydrophobic fluorinated solvent, a binder comprising a hydrophobicfluorinated polymer, hydrophobic fumed silica nanoparticles, andoptionally, hydrophobic aerogel nanoparticles. In some embodiments, thebinder is present in about 0.3 to about 1.5 weight percent of thecomposition. In other embodiments, the hydrophobic fumed silicananoparticles are present in about 0.01 to about 0.5 weight percent ofthe composition.

In another aspect, the present disclosure provides a structure includinga substrate and a superhydrophobic coating on at least a portion of thesubstrate. The superhydrophobic coating may include a hydrophobicfluorinated solvent, a binder comprising a hydrophobic fluorinatedpolymer, hydrophobic fumed silica nanoparticles, and optionally,hydrophobic aerogel nanoparticles. The substrate may be an opticallytransparent substrate such as glass or plastic.

In another aspect, the present disclosure provides a method for making acomposition. The method includes combining a hydrophobic fluorinatedsolvent, a binder comprising a hydrophobic fluorinated polymer, fumedsilica nanoparticles, and optionally, hydrophobic aerogel nanoparticles,mixing the combination, and drying the mixture to provide thecomposition.

In another aspect, the present disclosure provides a method for coatinga substrate with a composition. The method includes depositing a silaneon at least a portion of a substrate, and depositing a composition on atleast a portion of a surface of the deposited silane. The compositionmay include a hydrophobic fluorinated solvent, a binder comprising ahydrophobic fluorinated polymer, hydrophobic fumed silica nanoparticles,and optionally, hydrophobic aerogel nanoparticles.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a view of an example superhydrophobic optical thinfilm, including the various thin film layers and associated hydrophobicnanoparticles, according to aspects of the present disclosure.

DETAILED DESCRIPTION

The following detailed description describes various features andfunctions of the disclosed methods, compositions, and structures. Theillustrative embodiments described herein are not meant to be limiting.It will be readily understood that certain aspects of the disclosedmethods, compositions, and structures can be arranged and combined in awide variety of different configurations, all of which are contemplatedherein.

A superhydrophobic composition that is easily applied and well-bondedwithout sacrificing hydrophobicity or optical transparency is described.“Superhydrophobic,” as used herein, describes surfaces or coatings thathave a water contact angle of at least about 130°. Also as used herein,an “optically transparent” coating transmits at least about 90% ofincident light having a wavelength in the range of 300 nm to 1500 nm.“Well-bonded,” as used herein, refers to a composition, that whenapplied as a coating or thin film to a substrate, adheres to thesubstrate so as to not be easily removed with small amounts of shearforce (e.g., rubbing) or by exposure to environmental conditions (e.g.,sun, rain, wind, etc.).

In one aspect, the present disclosure provides a composition including

a hydrophobic fluorinated solvent;

a binder comprising a hydrophobic fluorinated polymer;

hydrophobic fumed silica nanoparticles, and

optionally, hydrophobic aerogel nanoparticles.

The hydrophobic fluorinated solvent may be a fluorinated materialcapable of dissolving the binder described herein. To provide goodoptical clarity of the resulting film or coating, it is beneficial thatthe composition include particles that are well-dispersed throughout thedeposition process. Particles that are too large or poorly dispersed canlead to clouding of the superhydrophobic surface. Desirable dispersionmay be achieved by using a suitable hydrophobic fluorinated solvent,which may act as a dispersive agent. In some embodiments, thehydrophobic fluorinated solvent may include a fluorinated alkane,fluorinated trialkylamine, fluorinated cycloalkane, fluorinatedheterocycloalkane, or combination thereof. In some embodiments, thefluorinated component may be perfluorinated. Suitable fluorinatedsolvents are commercially available from a number of sources, such as 3M(Maplewood, Minn.). Suitable fluorinated solvents include, for example,Fluorinert™FC-40, Fluorinert™ FC-43, Fluorinert™ FC-75, Fluorinert™FC-770, or an equivalent or similar material.

The fluorinated polymer binder may include a hydrophobic, fluorinatedpolymer that is capable of being dissolved in the hydrophobicfluorinated solvent described herein. The binder may enable thehydrophobic particles to adhere to the surface of a substrate, but ifthe binder is not selected properly or is used in the wrong amount, thebinder may affect the optical clarity of the resulting film or coating.The fluorinated polymer binder is preferably optically clear andamorphous. In some embodiments, the fluorinated polymer binder may be afluroalkyl polymer, fluoroalkoxy polymer, perfluoroalkyl polymer,perfluoroalkoxy polymer, or combination thereof. Suitable fluorinatedpolymer binders are commercially available from a number of sources,such as Solvay (Brussels, Belgium). Suitable fluorinated polymer bindersmay include, for example, Teflon® AF and Hyflon® AD.

The amount of the binder in the composition is related to the ability ofthe composition to form a film or coating with the desiredsuperhydrophobic, optical transparency and well-bonded propertiesdescribed herein. If too much binder is used in the composition, thenanoparticles may be engulfed by the binder to such a degree that thesurface loses its nanotexturing and thus its superhydrophobicproperties. If too little binder is employed, the nanoparticles may notbe effectively bonded to the substrate, and the adherence to thesubstrate may be affected. In some embodiments, the fluorinated polymerbinder is present in about 0.3 to about 1.5 weight percent of thecomposition. In other embodiments, the binder is present in about 0.8 toabout 1.2 weight percent of the composition. The binder may also bepresent in about 0.3 to about 1.4 weight percent, about 0.4 to about 1.5weight percent, about 0.3 to about 1.3 weight percent, about 0.4 toabout 1.3 weight percent, about 0.4 to about 1.2 weight percent, about0.5 to about 1.2 weight percent, about 0.5 to about 1.1 weight percent,about 0.5 to about 1.0 weight percent, about 0.6 to about 1.0 weightpercent, about 0.7 to about 1.4 weight percent, about 0.5 to about 1.5weight percent, about 0.5 to about 1.2 weight percent, or about 0.3 toabout 0.9 weight percent of the composition.

The hydrophobic fumed silica nanoparticles may be silica nanoparticleschemically modified with a hydrophobic silane. Suitable hydrophobicfumed silica nanoparticles are generally high surface area,nanostructured and/or nanoporous particles with an average particle sizeof about 200 nm or less. The average fumed silica nanoparticle sizerepresents an average linear dimension of the particles (e.g., anaverage diameter in the case of substantially spherical particles), andit may represent an average grain or crystallite size, or, in the caseof agglomerated particles, an average agglomerate size. In someembodiments, the average fumed silica nanoparticle size may be less thanabout 100 nm, less than about 75 nm, or less than about 50 nm. However,extremely small fumed silica nanoparticles (e.g., a few nanometers orless) may be difficult to disperse. In some embodiments, the averagefumed silica nanoparticle size is from about 10 nm to about 200 nm, fromabout 25 nm to about 100 nm or from about 40 nm to about 60 nm. In someembodiments, the nanoparticles are chemically treated with a fluorinatedmaterial. In other embodiments, the nanoparticles are chemically treatedwith polydimethylsiloxane (PDMS). U.S. Patent Publication No. US2006/0110542 discloses several types of modified fumed silica, and isincorporated by reference. Colloidal silicon dioxide made from fumedsilica is prepared by a suitable process to reduce the particle size andmodify the surface properties. The surface properties are modified toproduce fumed silica by production of the silica material underconditions of a vapor-phase hydrolysis at an elevated temperature with asurface modifying silicon compound (e.g., silicon dimethylbichloride).The hydrophobic properties of the fumed silica nanoparticles are aresult of treatment with at least one compound selected from the groupconsisting of organosilanes, fluorinated silanes, and disilazanes.

Suitable organosilanes include, but are not limited toalkylchlorosilanes; alkoxysilanes, e.g., methyltrimethoxysilane,methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane,n-propyltrimethoxysilane, n-propyltriethoxysilane,i-propyltrimethoxysilane, i-propyltriethoxysilane,butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane,octyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane,n-octyltriethoxysilane, phenyltriethoxysilane, and polytriethoxysilane;trialkoxyarylsilanes; isooctyltrimethoxy-silane;N-(3-triethoxysilylpropyl)methoxyethoxyethoxy ethyl carbamate;N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethyl carbamate;polydialkylsiloxanes including, e.g., polydimethylsiloxane; arylsilanesincluding, e.g., substituted and unsubstituted arylsilanes; alkylsilanesincluding, e.g., substituted and unsubstituted alkyl silanes including,e.g., methoxy and hydroxy substituted alkyl silanes; and combinationsthereof. Suitable alkylchlorosilanes include, for example,methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane,octylmethyldichlorosilane, octyltrichlorosilane,octadecylmethyldichlorosilane and octadecyltrichlorosilane. Othersuitable materials include, for example, methylmethoxysilanes such asmethyltrimethoxysilane, dimethyldimethoxysilane andtrimethylmethoxysilane; methylethoxysilanes such asmethyltriethoxysilane, dimethyldiethoxysilane and trimethylethoxysilane;methylacetoxysilanes such as methyltriacetoxysilane,dimethyldiacetoxysilane and trimethylacetoxysilane; vinylsilanes such asvinyltrichlorosilane, vinylmethyldichlorosilane,vinyldimethylchlorosilane, vinyltrimethoxysilane,vinylmethyldimethoxysilane, vinyldimethylmethoxysilane,vinyltriethoxysilane, vinylmethyldiethoxysilane andvinyldimethylethoxysilane.

Suitable fluorinated silanes include fluorinated alkyl-, alkoxy-, aryl-and/or alkylaryl-silanes, and fully perfluorinated alkyl-, alkoxy-,aryl- and/or alkylaryl-silanes. An example of a suitable fluorinatedalkoxy-silane is perfluorooctyltrimethoxysilane.

Suitable disilazanes include, for example, hexamethyldisilazane,divinyltetramethyldisilazane andbis(3,3-trifluoropropyl)tetramethyldisilazane. Cyclosilazanes are alsosuitable, and include, for example, octamethylcyclotetrasilazane.

Suitable hydrophobic fumed silica nanoparticles are commerciallyavailable from a number of sources, including Cabot Corporation(Tuscola, Ill.) under the trade name CAB-O-SIL, and Degussa, Inc.(Piscataway, N.J.), under the trade name AEROSIL. Suitable hydrophobicfumed silica particles include, for example, AEROSIL[R]R 202,AEROSIL[R]R 805, AEROSIL[R] R 812, AEROSIL[R]R 812 S, AEROSIL[R] R 972,AEROSIL[R]R 974, AEROSIL[R]R 8200, AEROXIDE [R] LE-1 and AEROXIDE [R]LE-2.

In some embodiments, the hydrophobic fumed silica nanoparticles arepresent in about 0.01 to about 0.5 weight percent of the composition. Inother embodiments, the hydrophobic fumed silica nanoparticles arepresent in about 0.08 to about 0.12 weight percent of the composition.The hydrophobic fumed silica nanoparticles may also be present in about0.03 to about 0.5 weight percent, about 0.04 to about 0.5 weightpercent, about 0.03 to about 0.4 weight percent, about 0.04 to about 0.4weight percent, about 0.04 to about 0.3 weight percent, about 0.05 toabout 0.2 weight percent, about 0.05 to about 0.1 weight percent, about0.05 to about 0.1 weight percent, about 0.06 to about 0.1 weightpercent, about 0.07 to about 0.1 weight percent, about 0.05 to about 0.5weight percent, about 0.05 to about 0.3 weight percent, or about 0.01 toabout 0.09 weight percent of the composition.

In some embodiments, the composition may further include hydrophobicaerogel nanoparticles. The combination of hydrophobic fumed silicananoparticles in conjunction with hydrophobic aerogel nanoparticles mayprovide a coating or film with additional water repellency.Superhydrophobic coatings that include hydrophobic aerogel nanoparticlesbut without fumed silica nanoparticles can provide superhydrophobic,optically clear thin films. But these films fall apart with smallamounts of shear force. Thus, such coatings are easily destroyed byrubbing, and do not provide prolonged protection to the coated surface.A composition including hydrophobic fumed silica nanoparticles, however,provides a more durable superhydrophobic coating, which can be wellbonded to a glass surface. Combining hydrophobic aerogel withhydrophobic fumed silica allows the aerogel to be protected from rubbingshear forces by “hiding” between well-bonded fumed silica nanoparticles(See FIG. 1). The addition of hydrophobic aerogel nanoparticles canfurther increase the film's superhydrophobic behavior while maintaininggood durability.

Suitable hydrophobic aerogel nanoparticles are very high surface area(600-800 m²/g) particles with a density between about 100 and 200 kg/m³and an average particle size of about 200 nm or less. The averageaerogel nanoparticle size represents an average linear dimension of theparticles (e.g., an average diameter in the case of substantiallyspherical particles), and it may represent an average grain orcrystallite size, or, in the case of agglomerated particles, an averageagglomerate size. In some embodiments, the average aerogel nanoparticlesize may be less than about 100 nm, less than about 75 nm, or less thanabout 50 nm. However, extremely small aerogel nanoparticles (e.g., a fewmicrometers or less) may be difficult to disperse. In some embodiments,the average aerogel nanoparticle size is from about 10 nm to about 200nm, from about 25 nm to about 100 nm or from about 40 nm to about 60 nm.

The hydrophobic aerogel nanoparticles may be obtained from a precursorpowder that is processed to reduce the average particle size to about200 nm or smaller. The hydrophobic aerogel nanoparticles may includenanoscale surface asperities, i.e., a nanoscale surface texturecharacterized by protruding or sharp features separated by recessedfeatures and/or pores at the particle surface. Coating compositionsincluding particles with such nanoscale surface asperities may yieldcoatings with higher water contact angles and thus enhancedhydrophobicity. As one of ordinary skill in the art would recognize, thescale of the surface texture is smaller than the average size of theparticle; generally, surface asperities are at least about 50% smaller.For example, aerogel particles of about 100 nm in average particle sizemay include surface asperities of about 25 nm in average size or less,and hydrophobic particles of about 50 nm in average particle size mayinclude surface asperities of about 25 nm in size or less.

Suitable aerogel precursor powders are commercially available from anumber of sources, including Cabot Corp. (Boston, Mass.). Suitableaerogel precursor powders are sold under the Nanogel Aerogel, LUMIRA®Aerogel and ENOVA® Aerogel trade names, and include, for example ENOVA™Aerogel IC 3110, ENOVA™ Aerogel MT 1100, ENOVA™ Aerogel MT 1200, ENOVA™Aerogel IC 3120. These porous, nanostructured particles are available inparticle sizes ranging from about 5 microns to 4 mm, but may bemechanically milled or sonicated as discussed below to obtain particlesof reduced sizes (e.g., less than about 50 nm) for use in formingsuperhydrophobic coatings.

In another aspect, the present disclosure provides a structure includinga substrate and a superhydrophobic coating on at least a portion of thesubstrate. When the coating is on the substrate, the resulting film issuperhydrophobic, optically clear and well-bonded to the substrate. Thesuperhydrophobic coating may have a water contact angle of at least 130degrees. In some embodiments wherein the superhydrophobic coating has awater contact angle of at least 150 degrees. For example, the watercontact angle may be at least 130 degrees, at least 135 degrees, atleast 140 degrees, at least 145 degrees, at least 150 degrees, at least155 degrees, at least 160 degrees, at least 165 degrees, at least 170degrees or at least 175 degrees. In some embodiments, the water contactangle encompasses both advancing and receding water contact angles.

In some embodiments, the he superhydrophobic coating may have a lighttransmission of at least 95% for wavelengths between 300 nm and 1500 nm,or for visible wavelengths between 400 nm and 700 nm. The structure ofclaim 11, wherein the superhydrophobic coating has a light transmissionof at least 95% for wavelengths between 400 nm and 700 nm. The substratemay also be an optically transparent material such as glass or plastic.In embodiments where the substrate is also optically transparent, thecoated substrate allows light (e.g., from a laser or optical sensor) tobe transmitted through the substrate and the superhydrophobic coatingwith limited interference. The superhydrophobic nature of the coatingmay also enable the substrate to stay clean and dry by limiting theability for water (e.g., rain) and dirt or dust from accumulating on thesurface.

The superhydrophobic coating may also adhere to the substrate in amanner that does not allow it to be removed by rubbing or by exposure toenvironmental conditions (e.g., sun, rain, wind, etc.). This aspect ofthe superhydrophobic coating allows a single application to remain onthe substrate for a prolonged period of time, and is a characteristicnot previously known for a superhydrophobic, optically transparentcoating.

In some embodiments, the structure further comprises a silane layerdisposed between the superhydrophobic coating and the substrate. Thesilane may be employed to modify the surface energy or wettability ofthe surface of the substrate prior to the application of thesuperhydrophobic composition. The silane may be a silicon containingcompound having linear alkyl, branched alkyl or aryl groups, includingdipodal silanes, and may be optionally fluorinated. In some embodiments,the silane is a hydrophobic silane. Suitable silanes include, forexample, organoethoxysilane, trimethoxysilane,(perfluorobutyl)ethyltriethoxysilane,(3,3,3-trifluoropropyl)trimethoxysilane and any fluorinated silanedescribed herein.

In another aspect, the present disclosure provides a method for making acomposition as described herein. The method involves:

-   -   (a) combining a hydrophobic fluorinated solvent, a binder        comprising a hydrophobic fluorinated polymer, fumed silica        nanoparticles, and optionally, hydrophobic aerogel        nanoparticles;    -   (b) mixing the combination; and    -   (c) drying the mixture to provide the composition.

In embodiments where the composition includes hydrophobic aerogelnanoparticles, the combination may further include hydrophobic aerogelnanoparticles added prior to mixing. Mixing by sonication, (e.g., with asonic probe) can be used to break up conglomerates of the hydrophobicfumed silica nanoparticles and/or the hydrophobic aerogel nanoparticles,for example, if the conglomerated nanoparticles are large enough toscatter a significant amount of light.

In another aspect, the present disclosure provides a method for coatinga substrate with a composition disclosed herein. The method involves:

(a) depositing a silane on at least a portion of a substrate; and

(b) depositing a composition on at least a portion of a surface of thedeposited silane.

The silane may help prepare the substrate for enhanced bonding with thecomposition, particularly where the substrate is highly hydrophilic(e.g., glass).

Unlike other well bonded, superhydrophobic, optically transparent thinfilms known in the art, the sprayable composition described herein hasthe added advantage of being easily handled and applied. Whileconventional compositions are often applied with complicated, expensive,and cumbersome processes such as physical vapor deposition, thecomposition described herein may be applied to the substrate by, forexample, spray coating, spin coating, or dip coating, or by any otherdeposition techniques known in the art. Typically, the composition isdeposited onto a clear substrate formed of an optically transparentmaterial, such as glass or acrylic, although other substrates may beused.

After depositing the coating formulation, the solvent may be removed byair drying or by heating the substrate and/or deposited composition at atemperature above the boiling point of the fluorinated solvent. Forexample, when Fluorinert™ FC-40 (b.p. of 165° C.) is used as thefluorinated solvent, the substrate may be heated to a temperature inexcess of 165° C. to promote the evaporation of the fluorinated solvent.

EXAMPLES Example 1: Formation of a Superhydrophobic Composition

An amorphous fluoropolymer binder is dissolved in a fluorinated solvent.

Hydrophobic fumed silica nanoparticles are added. Optionally,hydrophobic aerogel nanoparticles are added. The mixture is mixed with asonic probe to break up conglomerates of the hydrophobic fumed silicaparticles and the hydrophobic aerogel particles, and dried to providethe desired material. Table 1 lists example compositions and the amountsof each component as weight percent of the composition.

TABLE 1 Example Compositions Hydrophobic Hydrophobic Fluoropolymer FumedSilica Aerogel Composition No. Fluorinated Solvent Binder NanoparticlesNanoparticles A Fluorinert ™ FC-40 Hyflon ® AD Aerosil ® ENOVA ® (1.0%)(0.5%) Aerogel IC3100 (0.3%) B Fluorinert ™ FC-40 Hyflon ® AD Aerosil ®ENOVA ® (0.6%) (0.3%) Aerogel IC3100 (0.2%) C Fluorinert ™ FC-40Hyflon ® AD Aerosil ® ENOVA ® (0.5%) (0.3%) Aerogel IC3100 (0.2%) DFluorinert ™ FC-40 Hyflon ® AD Aerosil ® ENOVA ® (0.3%) (0.15%) AerogelIC3100 (0%)

It should be understood that arrangements described herein are forpurposes of example only. As such, those skilled in the art willappreciate that other arrangements and other elements can be usedinstead, and some elements may be omitted altogether according to thedesired results.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims, along with the fullscope of equivalents to which such claims are entitled. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting.

1-18: (canceled)
 19. A method for coating a substrate with acomposition, the method comprising: depositing a silane on at least aportion of a substrate; and depositing a composition on at least aportion of a surface of the deposited silane, wherein the compositioncomprises a hydrophobic fluorinated solvent; a binder comprising ahydrophobic fluorinated polymer; and hydrophobic fumed silicananoparticles.
 20. The method of claim 19, wherein the compositionfurther comprises hydrophobic aerogel nanoparticles.
 21. The method ofclaim 20, wherein the average size of the aerogel nanoparticles iswithin the range of 10 nm to 200 nm.
 22. The method of claim 19, whereinthe average size of the silica nanoparticles is within the range of 10nm to 200 nm.
 23. The method of claim 19, wherein the substrate isoptically transparent.
 24. The method of claim 23, wherein the substrateis glass.
 25. The method of claim 23, wherein the substrate is plastic.26. The method of claim 19, wherein the silane includes a linear alkylgroup, a branched alkyl group, or an aryl group.
 27. The method of claim19, wherein the silane is a dipodal silane.
 28. The method of claim 19,wherein the silane is a hydrophobic silane.
 29. The method of claim 19,wherein the silane is selected from the group consisting oforganoethoxysilane, trimethoxysilane,(perfluorobutyl)ethyltriethoxysilane, and(3,3,3-trifluoropropyl)trimethoxysilane.
 30. The method of claim 19,wherein the silane is a fluorinated silane.
 31. The method of claim 19,wherein the binder is present in about 0.3 to about 1.5 weight percentof the composition.
 32. The method of claim 19, wherein the hydrophobicfumed silica nanoparticles are present in about 0.01 to about 0.5 weightpercent of the composition.
 33. The method of claim 19, wherein thebinder is amorphous, optically clear and soluble in the hydrophobicfluorinated solvent.
 34. The method of claim 19, wherein the hydrophobicfumed silica nanoparticles are chemically treated with a fluorinatedmaterial.
 35. The method of claim 19, wherein the hydrophobic fumedsilica nanoparticles are chemically treated with polydimethylsiloxane(PDMS).
 36. The method of claim 19, wherein depositing the compositioncomprises applying the composition by spray coating, spin coating, ordip coating.
 37. The method of claim 19, further comprising: afterdepositing the composition, removing the fluorinated solvent.
 38. Themethod of claim 37, wherein removing the fluorinated solvent comprisesheating at least one of the substrate or the deposited composition to atemperature above the boiling point of the fluorinated solvent.